JP5307554B2 - Multilayer ceramic capacitor - Google Patents

Abstract

Provided is a dielectric ceramic in which, while achieving a dielectric constant epsilon of 500 or more, a breakdown voltage higher than 90 kV/mm can be obtained and which is suitable for constituting dielectric ceramic layers of a multilayer ceramic capacitor for medium-to-high voltage application. As the dielectric ceramic constituting dielectric ceramic layers of the multilayer ceramic capacitor, a dielectric ceramic including, as a main component, (Ba1-xCax)mTiO3 where 0.30<=x<=0.50, and 0.950<=m<=1.025 is used. Preferably, the dielectric ceramic further includes a rare-earth element in an amount of 1 to 14 parts by mole relative to 100 parts by mole of the main component, and further includes Mn, Mg, and Si, respectively, in amounts of 0.1 to 3.0 parts by mole, 0.5 to 5.0 parts by mole, and 1.0 to 5.0 parts by mole relative to 100 parts by mole of the main component.

Description

The present invention relates to a product layer ceramic capacitors, particularly, to a product layer ceramic capacitor suitable for use under a high electric field.

  Some multilayer ceramic capacitors are used under a high voltage of 250 to 1000 V, for example. In this case, depending on the thickness of each dielectric ceramic layer, a high voltage of 25 to 100 kV / mm is applied as an electric field. Therefore, there is a concern that the dielectric ceramic layer may be dielectrically broken in such a multilayer ceramic capacitor for medium and high voltage applications.

  As can be seen from the background described above, the dielectric breakdown voltage (BDV: the unit is kV / mm) is an important index for multilayer ceramic capacitors intended for medium and high voltage applications. BDV refers to the value of an electric field that causes dielectric breakdown when the electric field is raised, and is due to a phenomenon that is completely different from the life in a load test.

For example, Japanese Patent No. 3323801 (Patent Document 1) discloses a dielectric ceramic of interest to the present invention. Patent Document 1 discloses a (Ca, Sr, Ba) (Zr, Ti) O ₃ -based dielectric ceramic. This dielectric ceramic has reduction resistance and achieves an improvement in BDV while improving the linearity of capacity-temperature characteristics and the quality factor Q.

  In general, a material having a high BDV has a low dielectric constant ε. The dielectric ceramic described in Patent Document 1 is no exception and achieves a BDV of 120 kV / mm or more, while the dielectric constant ε is as low as about 100. For this reason, it is disadvantageous for miniaturization of the multilayer ceramic capacitor.

Therefore, development of dielectric ceramics that can provide high values for both BDV and dielectric constant ε is desired.
Japanese Patent No. 3323801

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer ceramic capacitor suitable not only for a high dielectric breakdown voltage but also for a medium-to-high-voltage application, which has a high dielectric constant ε and is composed of a dielectric ceramic. .

The present invention provides a multilayer body including a plurality of laminated dielectric ceramic layers and internal electrodes formed along a specific interface between the dielectric ceramic layers, and is electrically connected to a specific one of the internal electrodes. And an external electrode formed on the outer surface of the multilayer body. Here, in order to solve the technical problem described above , the dielectric ceramic is (Ba _1-x Ca _x ) _m TiO ₃ (0.30 ≦ x ≦ 0.50, 0.950 ≦ m ≦ 1.025). And at least one rare earth element selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, 1 to 14 mol parts are contained with respect to 100 mol parts of the components, and Mn, Mg and Si are added in an amount of 0.1 to 3.0 mol parts, 0.5 to It is characterized by containing 5.0 mol parts and 1.0-5.0 mol parts . The internal electrode is mainly composed of Ni.

  The present invention is particularly advantageously applied to a multilayer ceramic capacitor in which the electric field used is 25 to 100 kV / mm and the guaranteed breakdown voltage is greater than 90 kV / mm.

In the dielectric ceramic used to constitute the multilayer ceramic capacitor according to the present invention, Ba _m TiO ₃ and Ca _m TiO ₃ may not be completely dissolved but may be separated into two phases. Here, Ba _m TiO ₃ alone has a low dielectric breakdown voltage, but has a high dielectric constant ε. On the other hand, Ca _m TiO ₃ alone has a high dielectric breakdown voltage, but has a low dielectric constant ε. When x, which is the molar ratio of these, is selected in the range of 0.30 ≦ x ≦ 0.50 as described above, it is not a mere average of Ba _m TiO ₃ and Ca _m TiO ₃ , It is possible to draw out characteristics that have both advantages. As a result, by forming the multilayer ceramic capacitor using Yuden ceramic of this, for example, the dielectric constant ε can while obtaining a value of 500 or more, to ensure 90 kV / mm is greater than the breakdown voltage.

The dielectric ceramic for use in multilayer ceramic capacitor according to the present invention, as described above, since further includes a rare earth element of a predetermined amount, increase the synergy with _Ba m TiO ₃ and _Ca m TiO ₃ For example, it is possible to guarantee a dielectric breakdown voltage of 100 kV / mm or more while realizing a dielectric constant ε of 500 or more.

Further, the dielectric ceramic used in the multilayer ceramic capacitor of the present invention, as described above, further, Mn, since the Mg and Si are Nde predetermined amount including, by firing in a reducing atmosphere, as described above A dielectric constant ε and a breakdown voltage can be obtained. Therefore, good reliability can be ensured even in a multilayer ceramic capacitor having an internal electrode mainly composed of Ni , such as the multilayer ceramic capacitor according to the present invention .

1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Laminate 3 Dielectric ceramic layer 4,5 Internal electrode 8,9 External electrode

  FIG. 1 is a cross-sectional view showing a multilayer ceramic capacitor 1 according to an embodiment of the present invention.

  The multilayer ceramic capacitor 1 includes a multilayer body 2. The multilayer body 2 includes a plurality of laminated dielectric ceramic layers 3 and a plurality of internal electrodes 4 and 5 respectively formed along a plurality of specific interfaces between the plurality of dielectric ceramic layers 3. Yes.

  The internal electrodes 4 and 5 are preferably composed mainly of Ni. The internal electrodes 4 and 5 are formed so as to reach the outer surface of the laminate 2, but the internal electrode 4 that is drawn to one end face 6 of the laminate 2 and the internal electrode that is drawn to the other end face 7. 5 are alternately arranged inside the stacked body 2.

  External electrodes 8 and 9 are formed on the outer surfaces of the laminate 2 on the end faces 6 and 7, respectively. The external electrodes 8 and 9 are formed, for example, by applying and baking a conductive paste mainly composed of Cu. One external electrode 8 is electrically connected to the internal electrode 4 on the end face 6, and the other external electrode 9 is electrically connected to the internal electrode 5 on the end face 7.

  On the external electrodes 8 and 9, in order to improve the solderability, the first plating films 10 and 11 made of Ni or the like and the second plating film made of Sn or the like thereon are further formed as necessary. 12 and 13 are formed, respectively.

In such a multilayer ceramic capacitor 1, the dielectric ceramic layer 3 is mainly composed of ( Ba _1−x Ca _x ) _m TiO ₃ (0.30 ≦ x ≦ 0.50, 0.950 ≦ m ≦ 1.025). It is composed of a dielectric ceramic as a component.

In this dielectric becomes ceramic main component _{(Ba 1-x Ca x)} m TiO 3, and the Ba m TiO ₃ and _Ca m TiO _3, not all the solid solution, which may be separated into two phases. _And, for the Ba m TiO _3, alone, although the breakdown voltage (BDV) is low, a high dielectric constant epsilon. On the other _hand, for the Ca m TiO _3, alone, it is high BDV, epsilon is low. Therefore, the x is the presence molar ratio of these two, as described above, selecting the range of 0.30 ≦ x ≦ _0.50, rather than the average of the Ba m TiO ₃ and _Ca m TiO _3, both It was found that a characteristic that combines the advantages of both was obtained by the synergistic effect. For example, a BDV of 120 kV / mm or more can be realized while obtaining a value of 500 or more for ε, and a BDV greater than 90 kV / mm can be guaranteed at a minimum.

The dielectric ceramic constituting the dielectric ceramic layer 3 is further at least one selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. of a rare earth element, with respect to 100 moles of the main component parts of the above 1 to 14 molar parts including. Such a rare earth element has an effect of enhancing the above-described synergistic effect of Ba _m TiO ₃ and Ca _m TiO _3, and by adding a predetermined amount of the rare earth element, the compatibility level of high BDV and high ε is greatly increased. Can be improved. More specifically, for example, a BDV of 140 kV / mm or more can be realized while obtaining a value of 500 or more for ε, and a BDV of 100 kV / mm or more can be guaranteed at a minimum.

The dielectric ceramic constituting the dielectric ceramic layer 3 further contains Mn, Mg, and Si in an amount of 0.1 to 3.0 mol parts, 0.5 to 5 mol, respectively, with respect to 100 mol parts of the main component. 2.0 molar parts, and 1.0 to 5.0 molar parts including. Thus, when a predetermined amount of Mn, Mg, and Si is included, firing in a reducing atmosphere is required, and even in the multilayer ceramic capacitor 1 having Ni as a main component of the internal electrodes 4 and 5, high BDV and high ε And good reliability can be secured.

As described above, the dielectric ceramic constituting the dielectric ceramic layer 3 contains a rare earth element and / or Mn, Mg and Si in addition to the main component made of (Ba _1-x Ca _x ) _m TiO _3. In the slurry prepared for forming the ceramic green sheet to be the dielectric ceramic layer 3, in addition to the Ba _m TiO ₃ powder and the Ca _m TiO ₃ powder, a rare earth element oxide or a carbonate compound, etc. Powders and / or powders such as oxides or carbonates of Mn, Mg and Si are added.

  The dielectric ceramic according to the present invention may be substituted with Sr if Ba and Ca are 5 mol% or less, and substituted with Zr and / or Hf if Ti is 5 mol% or less. May be.

  Next, experimental examples carried out to confirm the effects of the present invention will be described.

[Experiment 1]
First, Ba _m TiO ₃ powder and Ca _m TiO ₃ powder synthesized by a solid phase method were prepared as starting materials for the main component. Also, as starting materials for the _{component, Y 2 O 3, La 2} O 3, CeO 2, Pr 6 O 11, Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 2 O ₃ , oxide powders of rare earth elements such as Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ were prepared, as well as MgO, MnO and SiO ₂ powders. .

Next, the Ba _m TiO ₃ powder and the Cam _m TiO ₃ powder prepared as described above were weighed so as to have the composition shown in Table 1, and these powders were mixed. As a result, the starting material powder of the accessory component was added. In Table 1, the addition amount of each rare earth element, Mg, Mn and Si oxide powder is shown in mole parts relative to 100 mole parts of the main component. Next, the above-mentioned mixed powder was mixed in water for 16 hours with a ball mill using PSZ media having a diameter of 2 mm to obtain a sufficiently dispersed slurry. The slurry was dried to obtain a dielectric ceramic raw material powder.

  Next, a polyvinyl butyral binder and ethanol were added to the raw material powder and mixed by a ball mill to obtain a ceramic slurry. This ceramic slurry was formed into a sheet by a doctor blade method to obtain a ceramic green sheet.

  Next, a conductive paste mainly composed of Ni was screen-printed on the ceramic green sheet to form a conductive paste film to be an internal electrode. Then, the 11 ceramic green sheets on which the conductive paste film was formed were stacked so that the side from which the conductive paste film was drawn was staggered to obtain a raw laminate.

Next, the raw laminate is heated to a temperature of 300 ° C. in a nitrogen atmosphere to burn the binder, and then a temperature of 1250 ° C. in a reducing atmosphere composed of H ₂ —N ₂ —H ₂ O gas. Was fired for 2 hours to obtain a sintered laminate. This laminate includes a dielectric layer obtained by sintering a ceramic green sheet and an internal electrode obtained by sintering a conductive paste film.

  Next, a conductive paste containing glass frit and containing Cu as a main component is applied to both end faces of the laminate, and baked at a temperature of 800 ° C. in a nitrogen atmosphere, and externally connected to the internal electrodes. An electrode was formed, and a Ni plating film and a Sn plating film were further formed on the external electrode to obtain a multilayer ceramic capacitor according to each sample.

The outer dimensions of the multilayer ceramic capacitor thus obtained were 2.0 mm in length, 1.2 mm in width and 0.5 mm in thickness. The thickness of the dielectric ceramic layer interposed between the internal electrodes was 10 μm. It was. Further, the number of dielectric ceramic layers effective for capacitance formation was 10, and the counter electrode area per dielectric ceramic layer was 1.3 mm ² .

The dielectric constant ε of the dielectric ceramic constituting the dielectric ceramic layer in the multilayer ceramic capacitor according to each of the above samples was determined from the capacitance of the multilayer ceramic capacitor measured under the conditions of 25 ° C., 1 kHz, and 1 V _rms . Further, the resistivity ρ of the dielectric ceramic constituting the dielectric ceramic layer was determined from the insulation resistance measured by charging a voltage of 300 V for 60 seconds at a temperature of 25 ° C. In addition, a DC voltage was applied to the multilayer ceramic capacitor while being boosted at a rate of 50 V / second to obtain BDV (average value).

Table 2 shows the dielectric constants ε, log ρ, and BDV obtained as described above. Table 2 also shows ε × (BDV) ² as an index for making it possible to quantitatively determine the compatibility between the dielectric constant ε and BDV.

As shown in Table 1, Samples 1 to 6 are compositions in which the ratio of Ba _m TiO ₃ / Cam _m TiO ₃ is changed in a composition not including a rare earth element. Among these samples 1 to 6, according to samples 2 to 5 where x is in the range of 0.30 to 0.50, ε of 500 or more and BDV of 120 kV / mm or more, A certain BDV greater than 90 kV / mm is guaranteed. On the other hand, in sample 1, since x is less than 0.30, BDV is 80 kV / mm, and it is impossible to guarantee over 90 kV / mm, which is a guideline for medium to high pressure. On the other hand, in sample 6, ε is less than 500, which is disadvantageous for miniaturization of the multilayer ceramic capacitor.

Samples 7 to 12 evaluate the effect of adding Dy as a rare earth element while comparing with Samples 1 to 6 described above. According to Samples 7 to 12, both ε and BDV are improved as compared with Samples 1 to 6, and this is noticeable in ε × (BDV) ² . If x is outside the range of 0.30 to 0.50, the effect of rare earth element addition becomes very small as in samples 7 and 12.

  Samples 13 to 17 are for changing the addition amount of the rare earth element Dy and evaluating the influence of the addition amount. When the amount of rare earth element added is in the range of 1 to 14 mol parts, ε and BDV equal to or higher than those of Samples 2 to 5 not containing the rare earth element are obtained.

  Samples 18 to 21 are obtained by changing m. In samples 18 and 21 where m is out of the range of 0.950 to 1.025, the sinterability is deteriorated and ρ is lowered, which is not practical.

  Samples 22 to 33 are obtained by changing the addition amount of Mg, Mn, or Si. Samples 22 and 25 out of the range of 0.5 to 5.0 mole parts for Mg, Samples 20 and 29 out of the range of 0.1 to 3.0 mole parts for Mn, and 1.0 to 5 for Si In the samples 30 and 33 outside the range of 0.0 mol part, ρ decreases and becomes impractical.

  Samples 34 to 47 have been confirmed to be applicable to other rare earth elements than Dy.

[Experiment 2]
Experimental Example 2 is an experiment in which the starting material mixing method is changed while the composition is the same as each sample in Experimental Example 1. That is, the samples 101 to 147 produced in Experimental Example 2 have the same composition as Samples 1 to 47 in Experimental Example 1, respectively.

First, BaCO ₃ , CaCO ₃ and TiO ₂ powders are used as starting materials for the main components, and Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₆ O ₁₁ , Nd _{2 are used} as starting materials for the subcomponents. Rare earth elements such as O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ In addition to the oxide powders, MgO, MnO and SiO ₂ powders were prepared.

Next, only BaCO ₃ powder, TiO ₂ powder, rare earth oxide powder, and MgO powder were weighed to obtain compounded powder A. Similarly, only CaCO ₃ powder, TiO ₂ powder, rare earth element oxide powder and MgO powder were weighed separately to obtain a blended powder B. At this time, the content ratio of the Ba component of the blended powder A and the Ca component of the blended powder B was set to satisfy the value of x described in Table 1 in Experimental Example 1. The content ratio of the Ti component in the prepared powder A or B was set to satisfy the value of m described in Table 1 in Experimental Example 1 as compared with each Ba component or Ca component. Regarding the content ratio of the rare earth component, the contents shown in Table 1 in Experimental Example 1 were divided so that the ratio of the blended powder A: the blended powder B = 1-x: x. Regarding the content ratio of the Mg component, it was divided into mixed powders A and B in the same manner as the rare earth component.

  Next, the prepared powders A and B were mixed in water for 16 hours by a ball mill using PSZ media having a diameter of 2 mm to obtain fully dispersed slurries A and B, respectively. These slurries A and B were calcined at a temperature of 900 to 1100 ° C., respectively, to obtain calcined powders A and B, respectively.

Next, the calcined powder A and the calcined powder B are mixed, and powders of MnO and SiO ₂ which are subcomponents are added so as to have the same composition as in Experimental Example 1, and a PSZ medium having a diameter of 2 mm is used. Then, it was mixed in water for 16 hours by a ball mill to obtain a sufficiently dispersed slurry. This slurry was dried to obtain a dielectric ceramic raw material powder according to each sample.

  And using the dielectric ceramic raw material powder which concerns on each said sample, the same process as the case of Experimental example 1 was followed, and the multilayer ceramic capacitor concerning each of the samples 101-147 was obtained. For the multilayer ceramic capacitors according to these samples, the same items as in Experimental Example 1 were evaluated. The results are shown in Table 3.

  As can be seen by comparing Table 3 with Table 2, among the samples prepared in Experimental Example 2, at least the samples within the scope of the present invention are compared with Samples 1 to 47 prepared in Experimental Example 1, respectively. Thus, a larger BDV value is obtained.

[Experiment 3]
Experimental Example 3 is an experiment in which the starting material mixing method is changed to a method different from Experimental Example 2 while the composition is the same as each sample in Experimental Example 1. Samples 201 to 247 prepared in Experimental Example 3 have the same composition as Samples 1 to 47 in Experimental Example 1, respectively.

First, BaCO ₃ , CaCO ₃ and TiO ₂ powders are used as starting materials for the main components, and Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₆ O ₁₁ , Nd _{2 are used} as starting materials for the subcomponents. Rare earth elements such as O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ In addition to the oxide powders, MgO, MnO and SiO ₂ powders were prepared.

Next, only BaCO ₃ powder, CaCO ₃ powder, TiO ₂ powder, rare earth element oxide powder and MgO powder are weighed and prepared to have the same composition as in Experimental Example 1 except for Mn and Si, A blended powder was obtained.

  This prepared powder was mixed in water for 16 hours with a ball mill using PSZ media having a diameter of 2 mm to obtain a sufficiently dispersed slurry. The dried slurry was calcined at a temperature of 900 to 1100 ° C. to obtain a calcined powder.

Next, MnO and SiO ₂ powders, which are subcomponents, are added to the calcined powder so as to have the same composition as in Experimental Example 1, and using a PSZ media having a diameter of 2 mm, Mixing for a time, a well dispersed slurry was obtained. This slurry was dried to obtain a dielectric ceramic raw material powder according to each sample.

  And the dielectric ceramic raw material powder which concerns on each said sample was used, the same process as the case of Experimental example 1 was followed, and the multilayer ceramic capacitor concerning each of the samples 201-247 was obtained. For the multilayer ceramic capacitor samples according to these samples, the same items as in Experimental Example 1 were evaluated. The results are shown in Table 4.

  As can be seen by comparing Table 4 with Table 2, among the samples prepared in Experimental Example 3, at least the samples within the scope of the present invention are compared with Samples 1 to 47 prepared in Experimental Example 1, respectively. Thus, a larger BDV value is obtained.

Claims (2)

A laminate comprising a plurality of laminated dielectric ceramic layers and internal electrodes formed along a particular interface between the dielectric ceramic layers;
An external electrode formed on an outer surface of the laminate so as to be electrically connected to a specific one of the internal electrodes;
With
The dielectric ceramic layer is mainly composed of (Ba _1-x Ca _x ) _m TiO ₃ (0.30 ≦ x ≦ 0.50, 0.950 ≦ m ≦ 1.025), and further, Y, La At least one rare earth element selected from Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, Mn, Mg and Si are contained in 0.1 to 3.0 mol parts, 0.5 to 5.0 mol parts, and 1.0 to 5. mol, respectively, with respect to 100 mol parts of the main component. It consists of a dielectric ceramic containing 0 mole part ,
The internal electrode has Ni as a main component,
Multilayer ceramic capacitor. The multilayer ceramic capacitor according to claim 1 , wherein the electric field used is 25 to 100 kV / mm and the guaranteed breakdown voltage is greater than 90 kV / mm.

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